Radio goniometers and radio direction finders incorporating the same



July 28, 1964 HATCH 3,142,838

RADIO GONIOMETERS AND RADIO DIRECTION FINDERS INCORPORATING THE SAMEFiled Aug. 51, 1962 jun \N ENT/ZR BY nited States ate 3,142,838 RADIOGONIOMETERS AND RADIO DCTION FINDERS INCORPORATING THE SAME JamesFrederick Hatch, Hutton, Essex, England, assignor to The Marconi CompanyLimited, London, England, a British company Filed Aug. 31, 1962, Ser.No. 220,667 Claims priority, application Great Britain Nov. 23, 1961 6Claims. (Cl. 343-124) This invention relates to radio goniometers andradio direction finders incorporating the same and more particularly,although not exclusively, to such goniometers and direction findersintended for operation in the high frequency (H.F.) waveband extendingbetween the approximate limits of 2 mc./s. and 30 mc./ s.

In a conventional direction finder operating in the HF. band there arefour receiving aerials, symmetrically disposed on a circle having adiameter of approximately 0.4x where )t is the wavelength at the highestfrequency which the direction finder is designed to receive, andconnected to the two mutually perpendicular stator coils of a goniometerhaving a pick-up coil on its rotor, diametrically opposed aerials beingconnected to the opposite ends of a stator coil. For operation of thedirection finder over a frequency range of 2 mc./s.20 mc./s. twogoniometers are used, one for the upper part of the frequency band andone for the lower, in order to provide acceptable sensitivity andacceptably low errors. It is well known, of course, that sensitivity maybe improved by increasing the spacing of the aerials and that increasein spacing errors and ambiguities in the ascertained direction of areceived signal resulting from such increase in spacing may be avoidedby increasing the number of aerials. This, however, leads to therequirement of a goniometer having more than two stator coils-arequirement which has been regarded as very difiicult to satisfy dueboth to the danger of undesirable coupling between stator coils whichare not perpendicular to one another and the difiiculty, in a goniometerwhich is physically sufficiently small to operate satisfactorily at thehighest frequency in question, of providing adequate eificiency ofsignal transfer between the stator and rotor coils.

It is the object of this invention to provide improved radio goniometerswhich shall eifectively satisfy the above requirement and it is afurther object to provide improved radio direction finders which shallbe of increased sensitivity as compared with comparable known directionfinders.

According to this invention, a radio goniometer comprises two co-axialrelatively rotatable members, one within the other, the outer memberbeing formed of a ring-like ferrite body with at least two windingsequally spaced around the ring, the inner member being provided with awinding for magnetically coupling in turn, during rotation, with each ofsaid windings on the outer member, said winding on the inner memberbeing wound so as to progress initially in one direction andsubsequently in the opposite direction so that all the turns thereof areeffectively in parallel planes.

The expression ring like body is used in a wide sense to include anybody which circularly surrounds its straight axis. The section of thebody may be itself circular, i.e. the ring may be toroidal, but moregenerally the section will be of strip-like form, the body beingcylindrical.

Preferably at least the inner member is provided with a winding whichprogresses initially in one direction and subsequently in the oppositedirection so that all the turns thereof are effectively in parallelplanes. More preferably, however, both the inner and outer members areprovided with such windings.

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Preferably in the case of the inner member there are two such windingsconnected in parallel, one on each side of the centre line.

In a preferred construction the outer member is a stator of cylindricalform and is provided with four windmgs.

According to a feature of the invention, a radio direction finderincorporating a goniometer as above described comprises said goniometer,a plurality, equal to twice the number of windings on the goniometerouter member, of linear aerials equally spaced around a circle, meansfor connecting each pair of diametrically opposite aerials to theopposite ends of a corresponding winding on the outer member of saidgoniometer, and means for utilising signals derived from the winding onthe inner member of the goniometer for ascertaining the direction ofarrival of received radio waves.

The invention is further described with reference to the accompanyingdrawings in which FIGURES 1 and 2 are diagrammatic representations ofthe stator, and FIG- URE 3 a diagrammatic representation of the rotor,of a radio goniometer in accordance with this invention. FIGURE 4 showsdiagrammatically a direction finder incorporating the goniometer ofFIGURES 1, 2 and 3.

Referring to FIGURE 1, the goniometer stator comprises a ring-likeferrite body FS of cylindrical form carrying four windings wound aroundits section. Each winding is comprised of two half windings and thereare therefore, as illustrated, eight similar hald windings symmetricallydisposed on the ferrite cylinder. Each winding is made up of twodiametrically opposed half windings whereby one winding is constitutedby half windings 1 and 1, another by the half windings 2 and 2', a thirdby half windings 3 and 3', and a fourth by half windings 4 and 4. Thespacing of the turns of each winding and the spacing between adjacentwindings are preferably arranged to be equal, as shown, so that adjacentturns, whether on the same winding or on different windings, are equallyspaced from one another. In the illustrated example each half winding iscomprised of eight turns each embracing 5 of arc.

The interconnections between the half windings on the stator arerepresented in FIGURE 2 in which, for simplicity, only two halfwindings, together constituting a single stator winding, are shown. Itwill be seen from FIGURE 2 that the two half windings illustrated aresimilar windings and that they are interconnected in such manner thatthe magnetic fluxes in the ferrite cylinder FS, resulting from theapplication of a potential between the winding terminals T1 and T2,oppose one another whereby a concentrated magnetic field extendsdiametrically across the cylinder FS.

Conveniently the windings may be so arranged that connections may bemade to two of them, for example windings 1-1' and 3-3, at one end ofthe cylinder FS and connections made to the other two, for example 22'and 44', at the other end.

The goniometer rotor illustrated in FIGURE 3 comprises a hollow cylinderIR of insulating material carrying thereon two similar windings ofwhich, for simplicity in drawing, only one, the winding 5, is shown. Itwill be appreciated however that in addition to the illustrated windingwhich is wound on the left-hand side of the rotor as shown in thedrawing, there is another similar winding covering the right-hand sideof the rotor, the two windings being connected in parallel. As will beseen from the drawing, the turns of winding 5 lie approximately parallelto one another and progress towards the left, in the illustration, for 2/2 turns and in the opposite direction for the remaining 2 /2 turns. Asa result those parts of the winding 5 which have a component in thedirection of progression cancel one another out so that all the turns ofthe winding lie effectively parallel to one another.

The goniometer rotor-is of course provided with central spindles mountedin bearings and when completely assembled the rotor is coaxially withinthe stator with the rotor winding coupling in turn, during rotation,with the difierent stator windings. Output signals from the rotorWinding may conveniently be taken oif from the rotor by means ofslip-rings.

FIGURE 4 represents a direction finder in accordance with the presentinvention, incorporating a radio goniometer above described foroperation over a continuous frequency band of 2 mc./s.30 mc./s.Referring to FIG- URE 4, there are eight linear vertical aerials A1, A2,A3, A4, A1, A2, A3 and A4 symmetrically disposed around a circle havinga diameter of approximately 3/4)\ at a frequency of 25 mc./s. Theaerials are unbalanced unipole aerials and are mounted on the ground oron a simulated earth plane and have their bases insulated therefrom. Itwill be appreciated that diametrically opposite aerials, such forexample as'aerials A1 and A1, constitute together a directive aerial,the difference in the signals produced by the two aerials beingindicative of the direction of arrival of an incoming radio wave.Accordingly each oppositely disposed pair of aerials is connected viacoaxial cables to the opposite ends of a stator winding of goniometer G,which is a goniometer as illustrated in FIGURES 1, 2 and 3. Henceaerials A1 and A1 may be connected to half windings 1 and 1', aerials A2and A2 connected to half windings 2 and 2' and so on. As will beapparent, the output derived from the rotor winding of the goniometerwill vary in amplitude, as the rotor is turned, in dependence on thecorrespondence between the rotational position of the rotor and thedirection of arrival of the incoming wave, and the output of thegoniometer rotor is applied in the usual way to indicate apparatus 1A,as known per se.

In a practical case in which the spacing of diametrically opposedaerials was 9 metres and the height of each aerial was 6.1 metres, itwas found that a direction finder using a single goniometer as abovedescribed had a sensitivity over the range 225 mc./s. of from 0.5,uv./m. and a negligible spacing error. A comparable known directionfinder, on the other hand, having four symmetrically disposed aerialswith a spacing of 6.1 metres and employing two goniometers, one for thelower part of the frequency band and one for the upper part provided,over a wave band of 2-20 mc./s., a sensitivity of from 1-6 ,uv/m. andexhibited a spacing error at 20 mc./s. of 5.

I claim:

1. A radio goniometer comprising two coaxial relatively rotatablemembers, one Within the other, the outer member comprising a ring-likeferrite body with at least two windings equally spaced around the ring,the inner member having a winding for magnetically coupling in turn,during rotation, with each of said windings on the outer member, saidwinding on the inner member being wound so as to progress initially inone direction and subsequently in the opposite direction so that all theturns thereof are efiectively in parallel planes.

2. A radio goniometer as claimed in claim 1 wherein each winding on theouter member is wound around the section of said ferrite body andcomprises two diametrically opposite half-windings arranged to produceopposing magnetic fluxes in said ferrite body.

3. A radio goniometer as claimed in claim 2 wherein each winding on theouter member is wound so as to progress initially in one direction andsubsequently in the opposite direction so that each turn thereof iseffectively in a plane perpendicular to the part of the ferrite bodyabout which it is wound.

4. A radio goniometer as claimed in claim 1 wherein the inner member hastwo windings, one on each side of its center line, connected inparallel, each winding progressing initially in one direction andsubsequently in the opposite direction so that all the turns thereof areeffectively in parallel planes.

5. A radio goniometer as claimed in claim 1 wherein the outer member isa stator of cylindrical form and has four windings thereon.

6. A radio direction finder incorporating a radio goniometer as claimedin claim 1 and comprising said goniometer, a plurality, equal to twicethe number of windings on the goniometer outer member, of linear aerialsequally spaced around a circle, means for connecting each pair ofdiametrically opposite aerials to the opposite ends of a correspondingwinding on the outer member of said goniometer, and means for utilisingsignals derived from the winding on the inner member of the goniometerfor ascertaining the direction of arrival of received radio waves.

References Cited in the file of this patent UNITED STATES PATENTS2,985,876 Clough et al. May 23, 1961 FOREIGN PATENTS 773,235 GreatBritain Apr. 24, 1957

1. A RADIO GONIOMETER COMPRISING TWO COAXIAL RELATIVELY ROTATABLEMEMBERS, ONE WITHIN THE OTHER, THE OUTER MEMBER COMPRISING A RING-LIKEFERRITE BODY WITH AT LEAST TWO WINDINGS EQUALLY SPACED AROUND THE RING,THE INNER MEMBER HAVING A WINDING FOR MAGNETICALLY COUPLING IN TURN,DURING ROTATION, WITH EACH OF SAID WINDINGS ON THE OUTER MEMBER, SAIDWINDING ON THE INNER MEMBER BEING WOUND SO AS TO PROGRESS INITIALLY INONE DIRECTION AND SUB-